General harmony:
* Concord: Agreement or compatibility, especially in opinion or feeling.
* Agreement: A state of understanding or acceptance.
* Unity: The state of being united or joined together.
* Cohesion: The action or fact of uniting or sticking together.
* Balance: A state of equilibrium or stability.
* Peace: Freedom from disturbance; tranquility.
* Congruence: Agreement or consistency between things.
Harmony in music:
* Consonance: A pleasing combination of sounds.
* Euphony: A pleasing combination of sounds.
* Melody: A pleasing sequence of notes.
Harmony in relationships:
* Compatibility: The ability to exist or occur together without conflict.
* Understanding: Shared knowledge, information, or meaning.
* Empathy: The ability to understand and share the feelings of another.
* Trust: Firm belief in the reliability, strength, or truth of someone or something.
* Respect: A feeling of deep admiration for someone or something elicited by their abilities, qualities, or achievements.
Harmony in nature:
* Balance: A state of equilibrium or stability.
* Interdependence: The state of being mutually dependent.
* Synergy: The interaction or cooperation of two or more organizations, substances, or other agents to produce a combined effect greater than the sum of their separate effects.
The best word to use will depend on the specific context and the nuances of the meaning you wish to convey.